Syngamus trachea, also called gapeworm, red worm or fork worm, is a parasitic roundworm that infects the respiratory system of poultry - chickens, turkeys, pigeons, guinea fowls, ducks, pheasants, quails, etc. - and numerous wild birds.
It is found worldwide, particularly in Asia and Africa. It is quite common in birds reared on soil in traditional farming: up to 25% of birds in a farm may be infected.
The disease caused by Syngamus trachea is called syngamiasis.
These species do not affect dogs, cats, cattle sheep, goats, swine or horses.
Are birds infected with Syngamus trachea contagious for humans?
- NO: The reason is that these worms are not human parasites.
Final location of Syngamus trachea
Predilection sites of Syngamus trachea are the trachea and the bronchi.
Anatomy of Syngamus trachea
Syngamus trachea is a medium-sized worm. Males are up to 6 mm, females up to 20 mm long. They have a red color. As in other roundworms, the body of these worms is covered with a cuticle, which is flexible but rather tough. The worms have a tubular digestive system with two openings. The mouth capsule is cup-shaped and has up to 10 teeth. The worms also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels. Each male has a bursa with two short spicules for attaching to the female during copulation.
Characteristic for these worms is that the adults live in permanent copulation. The shorter male being attached to the female results in a form like a "Y", hence the common name "fork worm".
The eggs are ellipsoid, ~45x80 micrometers, have a thick shell, a plug-like thickening at each pole, and contain approx. 16 cells.
Syngamus trachea has a direct life cycle, but with several facultative intermediate hosts (transport or paratenic hosts) such as earthworms, snails, slugs, and insects (e.g. flies, cockroaches).
Adult females lay eggs in the airways of infected birds. These eggs reach the bird's mouth (through coughing, exudations, etc.), are swallowed and passed with the feces. Once in the environment infective L3 larvae develop inside the eggs within 1-2 weeks. Once ingested by intermediate hosts, the eggs release the larvae that become encysted in the tissues and can remain infective for years.
Birds become infected through food or water contaminated with infective eggs, or after eating contaminated transport hosts (earthworms, snails, insects, etc). Once inside the bird, larvae in the gut cross its lining and reach the blood vessels. Subsequently they are carried towards the lungs along the mesenteric veins, the liver and the heart. They reach the lungs about 24 hours after infection. There they molt twice. Shortly after the last molt they copulate and migrate to the trachea where they attach to the wall to suck blood.
The prepatent period (time between infection and first eggs shed) is 12 to 14 days. Some larvae may reach the lungs directly across the body cavity, which extends the prepatent period.
Harm caused by Syngamus trachea, symptoms and diagnosis
Syngamus trachea can be very harmful, especially for young birds. They are usually not a problem in modern operations under confinement conditions. But they can be a serious problem in free-range poultry, particularly if the birds have access to humid environments with abundant intermediate hosts (earthworms, snails, etc.). These worms are often a problem in pheasant farms. In regions with a cold winter infections occur mainly during late spring and summer, along with the peaks in the populations of intermediate hosts.
A few worms are usually well tolerated, especially by adult birds, which usually develop natural resistance if previously exposed to the worms. But in heavy infections the worms cause inflammation of the wall of the trachea and an increased mucus production, sometimes mixed with blood leaking from the small injuries caused by the worms. Clinical signs include coughing, sneezing and respiratory disturbances. Initially the birds try to expel the worms vigorously shaking their heads. Later they repeatedly gape and breathe with a hissing sound. They refuse to drink, lose appetite and weight and become apathetic. Anemia can also occur. Deaths can happen, particularly in young birds.
Diagnosis can be confirmed in young birds through direct observation of the trachea against a strong light (after displacing the neck feathers and pulling the skin): adult worms can be seen inside the trachea. Characteristic eggs can also be detected in samples of the feces or of tracheal mucus.
Prevention and control of Syngamus trachea infections
In endemic regions it is highly recommended to keep the birds' bedding as dry as possible and to frequently change it, because survival of the worms' eggs needs humidity. It is also advisable to restrict the access of free-range poultry to dark and humid environments where intermediate hosts are usually more abundant. Outdoor cages should be equipped with adequate screens or nets that keep wild birds off, since they are carriers of worms. All these measures are especially important for young birds, which are likely to suffer more from Syngamus infections. Young birds should be reared separately from old birds that could carry worms even if they show no symptoms.
The use of insecticides or molluscicides to kill the intermediate hosts is usually not advisable. Populations of intermediate hosts that occur mainly outdoors (earthworms, grasshoppers, water fleas, etc.) are unlikely to be effectively controlled with pesticides, which are also highly detrimental for other beneficial organisms in the environment. Insecticides can be helpful against those intermediate hosts that develop indoors (e.g. cockroaches) but only those products that are approved for use on poultry facilities should be used.
Numerous classic broad spectrum anthelmintics are effective against Syngamus trachea, e.g. several benzimidazoles (albendazole, fenbendazole, flubendazole, mebendazole, oxfendazole, etc.), levamisole, as well as macrocyclic lactones (e.g. ivermectin).
For use on poultry these active ingredients are usually available as additives for feed or drinking water, seldom as injectables or tablets (mainly for single animal treatment, typical for fighting roosters).
Most such wormers kill the worms shortly after treatment and are quickly metabolized and/or excreted within a few hours or days. This means that they have a short residual effect, or no residual effect at all. As a consequence treated animals are cured from worms but do not remain protected against new infections. To ensure that they remain worm-free the animals have to be dewormed periodically, depending on the local epidemiological, ecological and climatic conditions.
So far no vaccine is available against Syngamus trachea. To learn more about vaccines against parasites of livestock and pets click here.
Biological control of Syngamus trachea (i.e. using its natural enemies) is so far not feasible.
You may be interested in an article in this site on medicinal plants against external and internal parasites.
Resistance of Syngamus trachea to anthelmintics
There are so far a no reports on confirmed resistance of Syngamus trachea to anthelmintics.
This means that if an anthelmintic fails to achieve the expected efficacy against Syngamus trachea it is most likely that either the product was unsuited for the control of these worms, or it was used incorrectly.
Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Syngamus control.